This invention relates generally to printed images and methods for producing such images. More specifically, the present invention relates to methods and apparatus which are capable of printing high-quality image areas using less image-generating media, such as printer ink or toner.
Printing devices, such as ink-jet, laser and other types of printers, are widely used to reproduce and print images, such as images stored on a computer, onto printable media. Such devices generally generate images by transferring an image-generating medium, such as ink or toner, to the printable medium to form the images.
However, when producing images in this manner, certain areas on the printable medium, such as those corresponding to large areas of an image having a uniform color intensity, often receive a relatively large amount of ink or toner because of the density of the printed image in those areas. This is problematic because the amount of image-generating medium stored in printers is limited and the use of excessive ink or toner more rapidly depletes the stored medium. Because image-generating medium is cumbersome to handle, relatively expensive, and inconvenient to frequently replace, it is desirable to find a way to print image areas that appear to be of uniform color and intensity while conserving image-generating medium.
One method for conserving ink in ink-jet printers is disclosed in U.S. Pat. No. 5,706,414, issued to Pritchard. This patent describes a method of systematically and uniformly depleting non-edge pixels from an image such that less ink is used in printing the remaining pixels of the image. In this method, a rectangular array of binary flags having a set number of flags corresponding to pixels which are potential candidates for depletion is xe2x80x9ctiledxe2x80x9d or mapped onto all pixels of the undepleted image. Each potential depletion pixel is then tested to determine if it is an edge pixel. If the pixel is an edge pixel, it is not depleted. If it is a non-edge pixel, it is depleted. In this manner, a set number of pixels is essentially uniformly and abruptly depleted from each array mapped across the entire interior of an image.
However, the present inventor has come to appreciate that the method disclosed in Pritchard is disadvantageous for several reasons. One disadvantage is that because the depletion of pixels is essentially uniform across an image, the human eye is more likely to discern a degradation in the print quality of the image.
Recognizing this and other drawbacks of the prior art, the present inventor has perceived a need for a new and more desirable method for producing images using less ink, toner or other image-generating medium. These and other objects are achieved by the present invention as described below.
The present invention provides a method for reproducing areas of an image on a printable medium by defining the image area on the printable medium and depositing ink, toner or other image-generating media in the image area such that at least a first portion of the image area is printed by continually reducing the amount of image-generating medium deposited in the first portion from a predetermined amount at at least one outer edge of the first portion to a lesser amount at at least one virtual interior reduction edge of the first portion. In this manner, the present invention conserves a significant amount of image-generating medium while producing images which appear to the human eye to be of better quality than images generated by prior art ink-saving printing processes.
Although applicants do not necessarily intend to be bound by or to any particular theory of operation, the present invention is believed to take advantage of the operation of the neural networks of the human visual system which are sensitive to the gradients of color and intensity at the edges of a solid image area but less sensitive to the middle portion of a solid image area. As used herein, the term xe2x80x9csolidxe2x80x9d refers to images or portions of images that appear to be of substantially uniform color and intensity. By defining at least a portion of an area having distinct outer edges, and using a continuously reduced quantity of image-generating medium to print the portion toward its interior, the present invention uses less image-generating medium to generate what appears to be a solid area. Moreover, the effects of continuously reducing the amount of image-generating medium used toward the interior of the portion, as opposed to using a uniform reduction in the amount of medium used across the entire area, are less discernable to a viewer""s eyes.
One aspect of the present invention is a method for printing an image. In a preferred embodiment, the method comprises the steps of: (a) defining an image area on a printable medium; and (b) depositing image-generating media in the image area such that at least a first portion of the image area is printed by continually reducing the amount of image-generating medium deposited in the first portion from a predetermined amount at at least one outer edge of the first portion to a lesser amount at at least one virtual interior reduction edge of the first portion.